Say I play an E (not a chord)... it sounds a certain way. If I make it into a chord an play an E Major chord it sounds completely different. What would be the chord that sounds like the single E alone and how could I find this for any note?

The third (missing here) is called the character of the chord because it determines Major v. minor and how the chord leads. Without it, the chord lacks its character, and can substitute for either a Major or a minor chord ( but not a dimished or other exotic).

Also try the inversion of this with a fourth at the bottom. It's drier but still edgy.

There are keyboard patches and effects pedals that can supply these extra tones automatically.

Wow, how could you guess that OP was looking for power chords? Impressive.
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GauthierJun 11 '12 at 9:18

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I stole the germ from Ulf's answer, I think. The power chord essentially is the very bottom of the harmonic series (skipping the true fundamental, of course).
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luser droogJun 11 '12 at 17:39

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I'm as impressed as Gauthier. I thought about the fifth interval but didn't think of it as a chord, but hey it is! (Thanks also for the reading pointer regarding my thoughts.)
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Ulf ÅkerstedtJun 11 '12 at 22:20

In order not to mess with the qualities of a single tone, what comes to my mind is to simply add tones that are (likely) already present in the single tone: the tones of the overtone series!

So to keep the qualities of say E3, you could add E4, B4, E5, G#5, B5 and E6, composing an E major chord with an overtone matching voicing. (I'm skipping the D6 since it is a bit too much off from the nearby overtone, and also runs the risk of altering the character too much.)

But it's hard to tell what you think a single tone versus a chord sounds like, and what you expect of a chord that should sound like the qualities of a single tone.

I have a feeling that this is not what you are looking for. Or is it? -- As a related note I've always been amazed how the same tone can sound different, to me, in different places in a phrase or a melody. I've come to the conclusion that this is an effect of differing harmonic context as well as of the rhythmical context such as if it appears on a down beat or on an up beat etc. Yet another issue that amazes me is how the same specific interval can sound small respectively large depending on context.
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Ulf ÅkerstedtJun 10 '12 at 17:33

This is strange, I doubt that you can create a chord which will sound like an E alone, that's why one would just play an E. Your question appears to be kind of redundant. The purpose of a chord is to enrich harmonies in a piece, I guess the closest would be simply playing octaves.

It depends on what instrument. On certain instruments you can make overtones and have "phantom" notes which sound nicely, but other than that, you cannot make a distinct chord sound exactly like a single note since that is counter-intuitive.

Aside from power chords, if you need to find the chord for a single note, you're also going to need to take a look at the other notes.

In the most general of cases, you're going to be able to derive the scale/key of the melody; e.g. if the melody contains a F# and a C, chances are that it's going to be in the key of G Major/E minor. The so called 'circle of fifths' is a great way to visualize that - look it up.

Once you've got the key, you can pick chords from that key that match the note. For example, in the key of G, the note of E could work with Em (E-G-B), C (C-E-G), Am (A-C-E), and maybe also F#7 (F#-A#-C#-E - which has two out-of-key notes right there).

F#7 doesn't belong to the key of G (it's a substitution for F#dim), but still works - which only serves to prove that there are many exceptions to this rule, and it is no more than a general method of figuring stuff out in some cases.